Zinc finger gene nolz1 regulates the formation of retinal progenitor cells and suppresses the Lim3/Lhx3 phenotype of retinal bipolar cells in chicken retina

Retinal Development in a Precocial Bird Species, the Quail (Coturnix coturnix, Linnaeus 1758)

The quail (Coturnix coturnix, Linnaeus 1758), a notable model used in developmental biology, is a precocial bird species in which the processes of retinal cell differentiation and retinal histogenesis have been poorly studied. The purpose of the present research is to examine the retinogenesis in this bird species immunohistochemically and compare the results with those from previous studies in precocial and altricial birds. We found that the first PCNA-negative nuclei are detected at Stage (St) 21 in the vitreal region of the neuroblastic layer, coinciding topographically with the first αTubAc-/Tuj1-/Isl1-immunoreactive differentiating ganglion cells. At St28, the first Prox1-immunoreactive nuclei can be distinguished in the vitreal side of the neuroblastic layer (NbL), but also the first visinin-immunoreactive photoreceptors in the scleral surface. The inner plexiform layer (IPL) emerges at St32, and the outer plexiform layer (OPL) becomes visible at St35—the stage in which the first GS-immunoreactive Müller cells are distinguishable. Newly hatched animals show a well-developed stratified retina in which the PCNA-and pHisH3-immunoreactivies are absent. Therefore, retinal cell differentiation in the quail progresses in the stereotyped order conserved among vertebrates, in which ganglion cells initially appear and are followed by amacrine cells, horizontal cells, and photoreceptors. Müller glia are one of the last cell types to be born. Plexiform layers emerge following a vitreal-to-scleral gradient. Finally, our results suggest that there are no significant differences in the timing of different events involved in retinal maturation between the quail and the chicken, but the same events are delayed in an altricial bird species.

Timing and Distribution of Mitotic Activity in the Retina During Precocial and Altricial Modes of Avian Development

During development of the vertebrate retina, mitotic activity is defined as apical when is located at the external surface of the neuroepithelium or as non-apical when is found in more internal regions. Apical mitoses give rise to all retinal cell types. Non-apical mitoses are linked to committed horizontal cell precursors that subsequently migrate vitreo-sclerally, reaching their final position in the outer surface of the inner nuclear layer, where they differentiate. Previous studies have suggested differences in the timing of retinal maturation between altricial and precocial bird species. In the present study we analyze qualitatively and quantitatively the mitotic activity in the developing retina of an altricial (zebra finch, Taeniopygia guttata) and a precocial (Japanese quail, Coturnix coturnix) bird species. We found that pHisH3-immunoreactive apical and non-apical mitoses were abundant in the T. guttata retina at the hatching stage. In contrast, pHisH3 immunoreactivity almost disappeared from the quail retina at the embryonic day 10 (E10). Furthermore, we also found that the onset of the appearance of non-apical mitoses occurred at later stages in the altricial bird species than in the precocial one. The disappearance of apical mitoses and the spatiotemporal distribution of non-apical mitoses followed central to peripheral and dorsal to ventral gradients, similar to gradients of cell differentiation described in the retina of birds. Therefore, these results suggest that retinal neurogenesis is active at the hatching stage in T. guttata, and that horizontal cell differentiation is delayed in the altricial bird species compared to the precocial one. Together, this study reveals important insights into the timing differences that regulate bird retinal maturation and provides a better understanding of the evolution of avian altriciality and precociality.

LIM Homeobox 9 knockdown by morpholino does not affect zebrafish retinal development

LIM homeobox 9 (Lhx9) is a member of the LIM homeodomain transcription factor family, which expresses and functions in various vertebrate tissues, such as the gonads and pineal gland. Previous studies on lhx9 in zebrafish have mainly focused on the brain. However, little is known about the expression pattern of lhx9 during embryogenesis. Here, we detected lhx9 expression in zebrafish embryos using whole-mount in situ hybridization and found lhx9 expressed in heart, pectoral fin, and retina during their development in zebrafish. We then detailed the expression of lhx9 in retinal development. To further investigate the function of Lhx9 in retinogenesis, we performed morpholino (MO) knockdown experiments and found that upon lhx9 knockdown by MO, larvae presented normal eye development, retinal neural development, differentiation, proliferation, apoptosis, and responses to light stimulus. We not only elaborated the expression pattern of lhx9 in zebrafish embryogenesis, but we also demonstrated that lhx9 knockdown by morpholino does not affect the zebrafish retinal development, and our study provides data for further understanding of the role of Lhx9 in zebrafish retinal development.

Summary:lhx9 is expressed in the development of the zebrafish heart, pectoral fin, and retina, but lhx9 knockdown by morpholino does not affect zebrafish retinal development.

Transcriptome analysis of the zebrafish atoh7-/- Mutant, lakritz, highlights Atoh7-dependent genetic networks with potential implications for human eye diseases

Expression of the bHLH transcription protein Atoh7 is a crucial factor conferring competence to retinal progenitor cells for the development of retinal ganglion cells. Several studies have emerged establishing ATOH7 as a retinal disease gene. Remarkably, such studies uncovered ATOH7 variants associated with global eye defects including optic nerve hypoplasia, microphthalmia, retinal vascular disorders, and glaucoma. The complex genetic networks and cellular decisions arising downstream of atoh7 expression, and how their dysregulation cause development of such disease traits remains unknown. To begin to understand such Atoh7-dependent events in vivo, we performed transcriptome analysis of wild-type and atoh7 mutant (lakritz) zebrafish embryos at the onset of retinal ganglion cell differentiation. We investigated in silico interplays of atoh7 and other disease-related genes and pathways. By network reconstruction analysis of differentially expressed genes, we identified gene clusters enriched in retinal development, cell cycle, chromatin remodeling, stress response, and Wnt pathways. By weighted gene coexpression network, we identified coexpression modules affected by the mutation and enriched in retina development genes tightly connected to atoh7. We established the groundwork whereby Atoh7-linked cellular and molecular processes can be investigated in the dynamic multi-tissue environment of the developing normal and diseased vertebrate eye.

Behavioral Characterization of dmrt3a Mutant Zebrafish Reveals Crucial Aspects of Vertebrate Locomotion through Phenotypes Related to Acceleration

Vertebrate locomotion is orchestrated by spinal interneurons making up a central pattern generator. Proper coordination of activity, both within and between segments, is required to generate the desired locomotor output. This coordination is altered during acceleration to ensure the correct recruitment of muscles for the chosen speed. The transcription factor Dmrt3 has been proposed to shape the patterned output at different gaits in horses and mice.

Vertebrate locomotion is orchestrated by spinal interneurons making up a central pattern generator. Proper coordination of activity, both within and between segments, is required to generate the desired locomotor output. This coordination is altered during acceleration to ensure the correct recruitment of muscles for the chosen speed. The transcription factor Dmrt3 has been proposed to shape the patterned output at different gaits in horses and mice. Here, we characterized dmrt3a mutant zebrafish, which showed a strong, transient, locomotor phenotype in developing larvae. During beat-and-glide swimming, mutant larvae showed fewer and shorter movements with decreased velocity and acceleration. Developmental compensation likely occurs as the analyzed behaviors did not differ from wild-type at older larval stages. However, analysis of maximum swim speed in juveniles suggests that some defects persist within the mature locomotor network of dmrt3a mutants. Our results reveal the pivotal role Dmrt3 neurons play in shaping the patterned output during acceleration in vertebrates.

Novel replisome-associated proteins at cellular replication forks in EBV-transformed B lymphocytes

Epstein-Barr virus (EBV) is an oncogenic herpesvirus and WHO class 1 carcinogen that resides in B lymphocytes of nearly all humans. While silent in most, EBV can cause endemic Burkitt lymphoma in children and post-transplant lymphoproliferative disorders/lymphomas in immunocompromised hosts. The pathogenesis of such lymphomas is multifactorial but to a large extent depends on EBV’s ability to aggressively drive cellular DNA replication and B cell proliferation despite cell-intrinsic barriers to replication. One such barrier is oncogenic replication stress which hinders the progression of DNA replication forks. To understand how EBV successfully overcomes replication stress, we examined cellular replication forks in EBV-transformed B cells using iPOND (isolation of Proteins on Nascent DNA)-mass spectrometry and identified several cellular proteins that had not previously been linked to DNA replication. Of eight candidate replisome-associated proteins that we validated at forks in EBV-transformed cells and Burkitt lymphoma-derived cells, three zinc finger proteins (ZFPs) were upregulated early in B cells newly-infected with EBV in culture as well as expressed at high levels in EBV-infected B blasts in the blood of immunocompromised transplant recipients. Expressed highly in S- and G2-phase cells, knockdown of each ZFP resulted in stalling of proliferating cells in the S-phase, cleavage of caspase 3, and cell death. These proteins, newly-identified at replication forks of EBV-transformed and Burkitt lymphoma cells therefore contribute to cell survival and cell cycle progression, and represent novel targets for intervention of EBV-lymphomas while simultaneously offering a window into how the replication machinery may be similarly modified in other cancers.

Cancer cells must overcome chronic replication stress, a central barrier to DNA replication. This is true also for cancers caused by Epstein-Barr virus (EBV). To understand how EBV overcomes this barrier to successfully drive cell proliferation, we isolated proteins associated with the cellular replication machinery in EBV-transformed B lymphocytes and identified several cellular proteins that had not previously been linked to DNA replication in cancer or healthy cells. Three of these were zinc finger proteins enriched at the replication machinery in EBV-transformed and EBV-positive Burkitt lymphoma-derived cells, upregulated in newly-infected B cells, and expressed at high levels in infected B cells from transplant recipients. These zinc finger proteins also contributed towards cell proliferation, survival, and cell cycle progression. While these proteins may also contribute to DNA replication in other cancers, they simultaneously represent potential targets in EBV-cancers, some of which are difficult to treat.

Generation and characterization of Lhx3GFP reporter knockin and Lhx3loxP conditional knockout mice

LHX3, a LIM-homeodomain transcription factor, is broadly expressed in the developing pituitary, spinal cord, medulla, retina and inner ear, and plays essential roles during embryonic development. Mice with homozygous Lhx3 null mutation exhibit failure in the formation of pituitary gland and die perinatally. To facilitate the functional study of Lhx3 in mice, we engineered and characterized two novel Lhx3 mouse strains: Lhx3GFP reporter knock-in and Lhx3loxP conditional knockout mice. Coimmunolabeling of LHX3 and GFP shows that the expression pattern of the knock-in GFP reporter recapitulates that of endogenous LHX3 in cochlea, vestibule, retina, and spinal cord. By crossing Lhx3loxP mice with the ubiquitous CMV-Cre mice, we have demonstrated a high efficiency of Cre recombinase-mediated removal of exons 3 to 5 of Lhx3, which encode the second LIM-domain and the HD domain of LHX3, resulting global knockout of Lhx3. Thus, Lhx3GFP and Lhx3loxP mice serve as valuable genetic tools to dissect the tissue-specific roles of Lhx3 at late-gestation and postnatal stages in mice.